I have no clue what this even means (I have no herpes outbreak or anything), but I'm going to assume it's not flattering. I'd like to say something snotty and then block him, but I'm drawing a blank. If you've got a good response, lay it on me. :)

ETA: I decided to go with kcunning's advice and just keep my mouth shut. I blocked him and reported him for harassment instead. But I liked everyone's suggestions! Y'all are much better with witty comebacks than I am! :)